ISL6398 Datasheet, PDF (15/57 Pages) Intersil Corporation – Programmable soft-start rate and DVID rate

ISL6398
IMON - IMON is the output pin of sensed, thermally compensated
(if internal thermal compensation is used) average current of VR0.
The voltage at the IMON pin is proportional to the load current and
the resistor value. When it reaches to 3.0V, it initiates an overcurrent
shutdown, while 2.5V IMON voltage corresponds to READ_IOUT
(8Ch) maximum reading. By choosing the proper value for the
resistor at IMON pin, the overcurrent trip level can be set lower than
the fixed internal overcurrent threshold. During dynamic VID, the
OCP function of this pin is disabled to avoid false triggering. Tie it to
GND if not used. Refer to “Current Sense Output” on page 25 for
more details.
AUTO - A resistor from the pin to ground sets the current
threshold of phase dropping for operation. The AUTO mode can be
permanently disabled by pulling this pin to ground or PMBus D4h[2].
See Table 2 on page 17 and Table 8 on page 32 for more details.
SM_PM_I2CLK - Synchronous clock signal input of
SMBus/PMBus/I²C.
SM_PM_I2DATA - I/O pin for transferring data signals
SMBus/PMBus/I²C and VR controller.
SM_PMALERT# - Output pin for transferring the active low signal
driven asynchronously from the VR controller to SMBus/PMBus.
VRSEL_ADDR - Register pin used to program VR address
(PMBus) and to determine 5m/step or 10mV/step mode.
NVM_BANK_BT - Register pin to select NVM memory bank to use
(up to 8 configuration banks) and boot voltage, which can be set
by this pin or the value stored in NVM bank.
Operation
The ISL6398 is the smallest 6-Phase PWM controller. It utilizes
Intersil’s proprietary Advanced Linear EAPP (Enhanced Active Pulse
Positioning) digital control scheme that can process voltage and
current information in real time for fast control and high speed
protection and realize digital power management capability and
flexibility. It achieves the extremely fast linear transient response
with fewer output capacitors and overcomes many hurdles of
traditional digital approach, which uses non-linear, discrete control
method for both voltage loop and current balance loop and runs into
beat frequency oscillation and non-linear response. The ISL6398 is
designed to cloud computing, networking, datacenter, and POL
applications. The system parameters and required registers are
programmable and can be stored into selected NVM_BANK via
PMBus, no firmware required. It allows up to 8 memory banks, i.e.,
8 different applications. This greatly simplifies the system design
for various platforms and lowers inventory complexity and cost by
using a single device.
In addition, this controller is compatible with phase doublers
(ISL6611A and ISL6617), which can double or quadruple the phase
count. For instance, the multi-phase PWM can realize up to
24-phase count system. A higher phase count system can improve
thermal distribution and power conversion efficiency at heavy load.
The ISL6398 also supports coupled (2-Phase CI) inductor design.
Refer to Intersil’s application note, AN1268 for detailed coupled
inductor discussion.
Multiphase Power Conversion
High Power processor load current profiles have changed to the
point that the advantages of multiphase power conversion are
impossible to ignore. The technical challenges associated with
producing a single-phase converter (which are both cost-effective
and thermally viable), have forced a change to the cost-saving
approach of multiphase. The ISL6398 controller helps reduce the
complexity of implementation by integrating vital functions and
requiring minimal output components. The typical application
circuits diagrams on pages 6 through 9 provide the top level views of
multiphase power conversion using the ISL6398 controller.
Interleaving
The switching of each channel in a multiphase converter is timed to
be symmetrically out-of-phase with each of the other channels. In a
3-phase converter, each channel switches 1/3 cycle after the
previous channel and 1/3 cycle before the following channel. As a
result, the 3-phase converter has a combined ripple frequency three
times greater than the ripple frequency of any one phase, as
illustrated in Figure 1. The three channel currents (IL1, IL2 and IL3)
combine to form the AC ripple current and the DC load current. The
ripple component has three times the ripple frequency of each
individual channel current. Each PWM pulse is terminated 1/3 of a
cycle after the PWM pulse of the previous phase. The DC
components of the inductor currents combine to feed the load.
To understand the reduction of ripple current amplitude in the
multiphase circuit, examine Equation 1, which represents an
individual channel’s peak-to-peak inductor current.
I_{p-p =} ^_---V----^I_--^N_---L--^–_{-----V-F---}^O_-S----^UW_----^T_---^_---V-^_---I-V-N---^O_----^U_-----^T_-
(EQ. 1)
In Equation 1, V_IN and V_OUT are the input and output voltages
respectively, L is the single-channel inductor value, and F_SW is
the switching frequency.
IL1 + IL2 + IL3, 7A/DIV
IL1, 7A/DIV
PWM1, 5V/DIV
IL2, 7A/DIV
IL3, 7A/DIV
PWM2, 5V/DIV
PWM3, 5V/DIV
1µs/DIV
FIGURE 1. PWM AND INDUCTOR-CURRENT WAVEFORMS FOR
3-PHASE CONVERTER
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FN8575.1
August 13, 2015